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<h3 class="section" id="Marking-Roots-for-the-Garbage-Collector"><span>23.4 Marking Roots for the Garbage Collector<a class="copiable-link" href="#Marking-Roots-for-the-Garbage-Collector"> &para;</a></span></h3>
<a class="index-entry-id" id="index-roots_002c-marking"></a>
<a class="index-entry-id" id="index-marking-roots"></a>

<p>In addition to keeping track of types, the type machinery also locates
the global variables (<em class="dfn">roots</em>) that the garbage collector starts
at.  Roots must be declared using one of the following syntaxes:
</p>
<ul class="itemize mark-bullet">
<li><code class="code">extern GTY(([<var class="var">options</var>])) <var class="var">type</var> <var class="var">name</var>;</code>
</li><li><code class="code">static GTY(([<var class="var">options</var>])) <var class="var">type</var> <var class="var">name</var>;</code>
</li></ul>
<p>The syntax
</p><ul class="itemize mark-bullet">
<li><code class="code">GTY(([<var class="var">options</var>])) <var class="var">type</var> <var class="var">name</var>;</code>
</li></ul>
<p>is <em class="emph">not</em> accepted.  There should be an <code class="code">extern</code> declaration
of such a variable in a header somewhere&mdash;mark that, not the
definition.  Or, if the variable is only used in one file, make it
<code class="code">static</code>.
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